1. Field of the Invention
The present invention relates generally to the field of auxiliary switches for indicating the position or state of a principal apparatus, such as an interrupter, contactor, switch, disconnect or the like. More particularly, the invention relates to a novel technique for optically sensing the position or state of a switch or other moveable device, capable of providing feedback or monitoring signals indicative of the state.
2. Description of Related Art
In the field of electrical contactors and similar devices, it is generally known to monitor and feedback electrical signals indicative of the position or actual state of moveable contacts or other moveable elements within the device. Because such devices are often remotely controlled, and may inadvertently be switched from one state to another, or malfunction by remaining in an undesired state, the feedback and monitoring signals provide operators and system controllers with information useful for confirming proper operation of the devices or for flagging improper operation.
In one known technique for providing a feedback signal of this type, an auxiliary switch is attached to the principal device, such as a contactor. An auxiliary switch actuator is coupled to the movable elements of the contactor. As the contactor is shifted between conducting and non-conducting positions, the movable elements of the contactor carry with them a moveable contact element or spanner attached to the actuator within the auxiliary switch housing. The auxiliary switch is thus also physically shifted between conducting and non-conducting positions. In the conducting position of the auxiliary switch, the movable contact element abuts stationary contacts to complete a current carrying path between the auxiliary switch leads. The leads may be wired to monitoring circuitry for normally open or normally closed operation so as to apply or interrupt an electrical signal indicative of the actual position of the principal device. An auxiliary switch generally of this type is available from the Allen-Bradley Company of Milwaukee, Wis. under the commercial designation Bulletin 195.
While such devices are useful in providing feedback and monitoring signals, they are not without drawbacks. In particular, depending upon the voltage applied to the auxiliary switch, the electrical contact required to reliably provide the feedback signal may not be ensured. Moreover, because environments in which such auxiliary devices are applied may be relatively harsh, dirt and debris accumulating on stationary or moveable contacts in the auxiliary switch may prevent the conducting path through the device from being reliably established. Where the voltage level applied to the auxiliary switch is sufficient to generate arcs as the moveable and stationary contacts are joined and separated, such dirt and debris may be cleared from the conducting path. However, in an increasing number of devices the voltage levels applied to the auxiliary switch are too low (e.g., 5 volts d.c.) to provide sufficient arcing for clearing the debris from the mating conductors. In addition, in certain applications, it may be undesirable to complete a physical contact between stationary and moveable contacts or to generate path-clearing arcs in order to generate a feedback or monitoring auxiliary signal.
There is a need, therefore, for an improved auxiliary switch which does not rely upon physical contact between moveable switching elements to provide feedback and monitoring signals indicative of the actual position or state of a principal device such as an electrical contactor. In particular, there is a need for an improved technique of generating feedback signals indicative of the state of such principal devices which is resistant to contamination in harsh environments and provides reliable feedback signals, particularly for automatic control systems integrated with the principal and auxiliary devices. Moreover, there is a need for a relatively compact, economical auxiliary switching device which can be utilized with contactors and other principal devices of existing design in a relatively straightforward manner.